Coeliac, relating to the abdomen, is the adjectival root of coeliac disease, in which the immune system reacts abnormally to gluten in genetically susceptible people. The reaction damages the lining of the small intestine, flattening the villi that absorb nutrients and causing malabsorption, diarrhoea, fatigue, and in children poor growth. The only treatment is a strict lifelong gluten-free diet, excluding wheat, barley, rye, and usually oats unless certified pure. Diagnosis requires blood tests and intestinal biopsy while the patient is still eating gluten. Awareness has grown hugely, improving diagnosis but also spreading confusion with non-coeliac gluten sensitivity.